1. Field of the Invention
The present invention relates to an AC servo system with a plurality of motor drives, wherein the motor drive is incorporated with a movement control unit for distributed movement control.
2. Description of Prior Art
The current multiple axes control architecture is centralized by an upper controller to control servo drive for linear/circular motion. The current multiple axes control architecture is demonstrated hereinafter with conventional wiring or high speed communication.
FIG. 1 shows a schematic diagram of a prior art centralized control system for multiple axes control. The command and I/O 14 control of the multiple axes interpolation for the servo drive 12 is dealt by the upper controller 16. The signal from each axis is connected to the servo drive 12 through conventional wiring. However, the above scheme has following advantages:
1. High cost: The performance of the upper controller 16 is demanding for more axes. The CPU (now shown) of the upper controller 16 is also requested with higher grade.
2. Limited axes number: The axes number of the servo drive 12 is limited by CPU grade and hardware channel number.
3. Complicated wiring: There are complicated wiring of A/D, D/A, command pulse, feedback pulse, digital I/O signals between upper controller 16 and servo drive 12.
4. Insufficient resolution: The command signal is limited by physical signals such as A/D conversion resolution and pulse frequency.
5. Environment interference: The analog signal tends to be interfered in factory environment.
6. Maintenance problem: The wires are more complicated when the axes number of the servo drive 12 is large. The inspection and maintenance are troublesome.
FIG. 2 shows the schematic diagram of a prior art control system for multiple axes control with high speed communication, where the wire between the upper controller 16 and servo drive 12 in FIG. 1 is replaced by a high speed communication network 18. The high speed communication network 18 has simple wiring and can prevent interference and enhance resolution. The servo drive 12 does not have interpolation ability for path commands such that the upper controller 16 needs to send intense interpolation commands (more than 1 KHz) to each axis to achieve path denseness. However, the network is also used for sending feedback position, current and I/O status besides position and speed commands. The data throughput is high when the axes number is high and the status of each axis needs monitoring. The bandwidth of the high speed communication network 18 needs at least 10 MHz, which induces following results.
1. Higher cost: High speed communication is more sensitive to noise and high-standard communication hardware such as optical fiber is needed in factory environment.
2. Special specification: The high speed communication network 18 involves specialized industry standard such as SSC-Netand Sercos. The system generally is purchased in package and it is difficult to be tailored by customers.